IEEE 1344

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IEEE 1344 is a standard that defines parameters for synchrophasors[1] for power systems.[2] The standard added extension to the IRIG-B time code to cover year, time quality, daylight saving time, local time offset and leap second information. IEEE 1344 was superseded by IEEE C37.118 in 2005 and the time extensions were adopted as part of the IRIG timing standard in the 2004 edition.[3]

IRIG-B timecode consists of 100 bits, repeated each second. Every tenth bit is a "position identifier", and most of the remainder encode the current time (date, hour, minute and second). Bits 60–68 and 70–78 are reserved for other uses; IEEE 1344 is such a use. It defines the bits as follows:

IEEE 1344 extensions to IRIG B[4]
Bit Weight Meaning
60 LSP Leap second pending at end of minute
61 LS Leap second type (0=add, 1=delete)
62 DSP DST change pending at end of minute
63 DST DST in effect
64 ± Time zone offset sign (0=+)
65 1 Time zone offset
66 2
67 4
68 8
69 P7
70 0.5
71 1 Time quality
(Binary, 0–15)
72 2
73 4
74 8
75 PAR Even parity of all preceding data bits
76 0 Unused
77 0
78 0
79 P8 Position identifier

The DST and leap warning bits are set no more than 59 seconds before the indicated change, and indicate the change at the end of the minute. During a leap second, the warning bit should be set, the seconds field should show "60", and the Straight Binary Seconds field should equal 60 + 60 × minutes + 3600 × hours. The next second, the leap second warning bit should be clear, and the SBS field will repeat. Since negative leap seconds have never happened, and almost certainly never will, the LS bit is always 0.

The clock quality indication is a binary value. 0 means the clock is locked to a UTC-traceable source, without specifying a particular accuracy, and 15 means the clock has failed and the time is not reliable. Values between 1 and 11 indicate the time is accurate to within 10x−10 seconds of UTC, i.e. x=1 indicates UTC±1  ns, while x=11 indicates UTC±10 s.

The time zone offset indicates the difference UTC – timecode, so UTC = timecode + offset. This value changes when DST is active. The Straight Binary Seconds field also jumps by 3600 when this happens.

(Note that the related standard C37.118-2005[5] uses the opposite sign convention for time zone offset: offset = timecode – UTC, UTC = timecode – offset.)

The parity bit is even parity over all data bits from 1 through 74. Marker bits are ignored (or, equivalently, read as 0).

The standard also calls for indicating 2 digits of year in bits 50–58, which has been incorporated into the latest revision of the IRIG standard itself.


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